The brake systems (electric brake systems) in which an electric motor is used as a drive source for a booster magnifying the tread force with which a brake pedal is depressed are widely known. Such electric brake systems are provided with a stroke simulator, which simulatively generates the brake reaction force to be applied to the brake pedal depressed by the driver. (See Patent Literature 1.) The stroke simulator is required to impart to the driver operation feelings similar to the operation feelings which the conventional brake pedal operating with the brake fluid imparts to the driver. A brake system disclosed in consideration of the above requirement is configured such that an elastic force (reaction force) generated by elastic deformation of two elastic members having different moduli of elasticity is applied as the brake reaction force to the brake pedal, and the brake system includes a stroke simulator which applies reaction force from each of the two elastic members to the brake pedal in correspondence with the amount of depression of the brake pedal. (See Patent Literature 2.)